Micromachined LC resonant sensors have design trade offs in size and sensitivity as well as size and coupling. Such sensors have to be carefully laid out to optimize sensitivity and read range. Meanwhile, a sensor's fabrication process needs to be low cost. Traditional sensor designs that connect separate inductor and capacitive transducer to form a LC resonant structure has two weaknesses: (1) the capacitor is put in the middle of the spiral inductor, reducing the coupling between sensor and reader; and (2) fabrication requires two photolithography steps.
Moreover, traditional coating techniques, such as spin coating, that utilize dissolution suffer from a lack of surface area resulting from the polymer filling gaps, rather than conforming to the surfaces. In addition, these traditional macroscopically thick coatings prevent or restrict capillary forces. As a result, their responsiveness to changes in liquid may the limited due to slow kinetic changes.
There is, therefore, a need for a self-resonant sensor that is more responsive to changes in a liquid, improves coupling between the sensor and reader, and is easier to fabricate.